We are currently investigating the distribution of cholinergic, GABAergic and glutamatergic neurons in the rat striatum and the relationship among these neuronal systems in this region of the brain, especially with respect to the striatal cholinergic interneurons. Distribution studies are performed on striatal samples obtained from frontal serial sections of the brain. The distribution of cholinergic interneurons has been assessed from determinations of choline acetyltransferase activity, choline uptake and muscarinic receptor binding. The regional distribution of GABAergic neurons has been evaluated from data obtained on GABA uptake, glutamate decarboxylase activity and GABA levels. Interactions between GABAergic and cholinergic neurons are currently being examined by a neurochemical/neuropharmacological approach. Similar studies are planned for future investigations into potential glutamatergic-cholinergic interactions in the striatum.